In such a lube oil, a gas oil, and a jet fuel among petroleum products, a cold flow property is important. For this reason, it is preferable that, in a base oil used for those products, such a wax component causing a deterioration of the cold flow property as normal paraffins or slightly branched iso-paraffins completely or partially removed or transformed into components other than the wax component. Recently, since a hydrocarbon obtained by using a Fischer-Tropsch synthesizing method (hereinafter, simply referred to as an FT synthesizing method) does not contain such an environmental load material as a sulfur compound, it has attracted attention as a feedstock oil for manufacturing a lube oil or a fuel. However, such a hydrocarbon also contains a large amount of the wax component.
As a dewaxing technique for removing the wax component from the hydrocarbon oil, a method of extracting the wax component by using a solvent such as a liquefied propane or MEK has been known. However, the method has problems in that operation cost thereof is high, the method is used for limited types of feedstock oils, and production yield is limited according to the types of the feedstock oil.
On the other hand, as a method of transforming the wax component in the hydrocarbon oil into an non-wax component, a catalytic dewaxing method of isomerizing normal paraffins in the hydrocarbon oil into iso-paraffins by contacting the hydrocarbon oil to the so-called bi-functional catalyst having a hydrogenation-dehydrogenation ability and an isomerization ability in the presence of hydrogen has been proposed. In addition, as the bi-functional catalyst used for the catalytic dewaxing method, a catalyst containing a solid acid, especially a molecular sieve composed of such a zeolite, and metals belonging to Groups 8-10 or Group 6 of the Periodic Table of the Elements, particularly, a catalyst where the aforementioned metal is supported on the molecular sieve has been proposed.
Although the catalytic dewaxing method can be effectively used as a method of improving the cold flow property of the hydrocarbon oil, a normal paraffin conversion needs to be sufficiently increased in order to obtain a fraction suitable for the lube-oil base oil or the fuel base oil. However, since the catalyst used for the catalytic dewaxing method has the cracking ability of hydrocarbon as well as the isomerization ability, in a case where the hydrocarbon oil is subjected to the catalytic dewaxing process, lightening of the hydrocarbon accompanied with the increase in the normal paraffin conversion proceeds. Therefore, it is difficult to obtain a desired fraction with a good yield. In particular, in case of manufacturing a high quality lube-oil base oil requiring a high viscosity index and a low pour point, it is very difficult to obtain a desired fraction with a good economical efficiency by using the catalytic dewaxing of the hydrocarbon oil. For this reason, in this field, a synthetic base oil such as a poly alpha-olefin has been widely used.
Due to such circumstances, in a field of manufacturing the lube-oil base oil and the fuel base oil, there is a demand for a catalytic dewaxing technology capable of producing a desired iso-paraffin fraction with a good yield from the hydrocarbon oil containing the wax component.
Until now, an approach for improving an isomerization selectivity of the catalyst used for the catalytic dewaxing has been attempted. For example, in the following Patent Document 1, there is disclosed a manufacturing process of a lube oil which is dewaxed by contacting a hydrocarbon raw material having straight chain or slightly branched chain and 10 or more carbon atoms to a catalyst composed of such a molecular sieve having a medium-sized one-dimensional pore structure and a crystal size of less than about 0.5μ as ZSM-22, ZSM-23, and ZSM-48 containing metal of Group VIII and the like.
Incidentally, the molecular sieve constituting the catalyst used for the catalytic dewaxing is generally manufactured by using a hydrothermal synthesis in the presence of an organic template having such as an amino group and an ammonium group in order to obtain a predetermined pore structure. Next, the synthesized molecular sieve is calcined at a temperature of about 550° C. or higher in the ambience containing a molecular oxygen to remove the contained organic template as disclosed in the final paragraph of Section 2.1. Materials of the following Non-Patent Document 1, page 453. Next, the calcined molecular sieve is typically subjected to an ammonium-type ion exchange process in an aqueous solution containing ammonium ions as disclosed in the final paragraph of Section 2.3. Catalytic Experiments of the following Non-Patent Document 1, page 453. Further, after the ion exchange, such metal components as metals belonging to Groups 8-10 of the Periodic Table of the Elements are loaded on the molecular sieve. Next, the metal component-loaded molecular sieve is subjected to a drying process and a molding process (if needed), then is charged into a reactor, and is calcined typically at a temperature of about 400° C. in the ambience containing a molecular oxygen. Next, it is subjected to a reduction treatment approximately at the same temperature by hydrogen or the like, so that it is provided with the catalyst activity as the bi-functional catalyst.    [Patent Document 1] U.S. Pat. No. 5,282,958    [Non-Patent Document 1] J. A. Martens et al., J. Catal. 239 (2006) 451